The invention relates to a motor arrangement, in particular a servo drive for an electronic steering system, wherein provision is made for an isolating relay module to switch one or more motor phases such that its/their current does not flow.
In the case of servo drives, in particular in electronic steering systems, which, for example, have a synchronous motor, the danger of said systems locking exists in the event of a short circuit in the motor phases so that the motor vehicle could become unsteerable in the aforementioned example. The reason for this lies in the fact that in the event of a short circuit, the motor operates in the generator mode so that a driver of the vehicle has to work against the generator's torque in addition to the entire steering forces on the steering axle.
In the case of a synchronous motor, the motor phases are frequently connected up in a star connection. In order to keep the generator from operating in the event of a short circuit in a phase, provision can be made for a mechanically or electronically configured star-point relay, which in the case of a fault separates the motor phases from each other at the neutral point.
A typical deficiency of mechanical relays is their lack of reliability due to mechanical fatigue, respectively locked up mechanical components, whereby the reliability in separating the motor phases is curtailed.
An increase in the reliability is made possible by the use of electronic relays. In order that said relay can also be used with difficult surrounding conditions, it has to be connected to the motor system in a suitable manner. Furthermore, the power transistors used in electronic star-point relays have a heat build-up during normal operation, which makes a suitable design necessary to assure the dissipation of the heat. For that reason, a suitable structural-design technology and connection method are required.